Evolution of cellular systems promise significant data rate increase in the future, to 1 Gb/s and higher. Higher data rates typically require larger system bandwidths. For the IMT (International Mobile Telecommunications) advanced (i.e. the fourth generation mobile communication) systems, bandwidths up to 100 MHz are being discussed. Unfortunately, the radio spectrum is a limited resource and since many operators and systems need to share the same radio resource, finding a free 100 MHz contiguous spectrum is problematic.
One way to address this issue is to aggregate multiple narrow bandwidths (or component carriers) as illustrated in FIG. 1, which can be contiguous or non-contiguous to aggregately achieve the wide bandwidth. In the example of FIG. 1, a 50 MHz bandwidth spectrum is achieved by aggregating individual narrower bandwidth component carriers, which in this instance are 20 MHz, 20 MHz, and 10 MHz wide carriers. One benefit of such a solution is that it is possible to generate sufficiently large bandwidth for supporting data rates up to and above 1 Gb/s. Furthermore, this solution also makes it possible to adapt the spectrum parts to various situations and geographical positions thus making such solution very flexible.
A straightforward evolution of current cellular systems, such as LTE (Long Term Evolution), to support contiguous and non-contiguous spectrum is to introduce multi-carriers. That is, for each spectrum “chunk” representing a “legacy LTE” system carrier, a “4G” user equipment can be made to be capable of receiving multiple number of LTE component carriers of different bandwidths transmitted at different carrier frequencies.
A user equipment needs to listen for layer 1 and 2 (L1, L2) control signals to know where (in frequency or subchannels) and/or when (in time) data packets are scheduled to the user equipment. In single bandwidth systems like the GSM and LTE, the control signals are signaled from a serving base station on a single carrier frequency of the serving cell.
The control signaling of the single bandwidth systems can be extended to the multi-carrier scenario. That is, the user equipment can listen to the entirety of the aggregated spectrum for the control signals. Although this approach seems to be straightforward, there can be a significant drawback in terms of the user equipment power consumption. The aggregated spectrum approach, especially the non-contiguous spectrum case, implies that the radio receiver architecture for the user equipment will become more complicated than for a user equipment that is capable of only receiving small and contiguous system bandwidths. The reason is that the front end radio needs to be able to suppress blocking signal in between the spectrum “chunks”. Different kind of radio architecture can be used to handle this problem. However, they typically accompany drawbacks in terms of power consumption compared to standard continuous system bandwidth receivers.